Two-coat single cure powder coating

Abstract

A representative sample of a primer and topcoat formulation (as shown in Table 5, for example) were each examined to compare their rheological behavior, with a blend of the topcoat and primer formulation (85% topcoat, 15% primer) used for comparison. The time and temperature dependence of the viscosity was measured on a strain-controlled rheometer using parallel plate geometry in dynamic mode, with an applied strain of 1% and 1 Hz frequency of oscillation. The data is represented as complex viscosity (Pa-s). For the primer and topcoat formulations, sample discs were prepared by compressing 0.3 g of the powder composition in a 13-mm plug mold at 1000 ram force for 15 seconds. Pressing was done at room temperature to avoid premature curing of the powder. The rheometer was set at 70° C. for sample loading. The gap was then set to 0.05 mm below the thickness of the pressed pellet to ensure contact with parallel plates. The temperature of the sample and fixtures were equilibrated for 10 minutes before measurements were taken. The sample temperature was ramped at 5° C./min from 70° C. to 245° C. to examine the rheological behavior as a function of temperature. The resultant curve of complex viscosity versus temperature and is examined to compare the flow behavior of the powder compositions.